1. Field of the Invention
The invention relates to a variable speed fan motor.
2. Description of the Related Art
A DC brushless permanent magnetic (BPM) motor is utilized to substitute a permanent-split capacitor (PSC) motor in current HVAC systems, so that advantages of a variable speed fan motor are realized, and it is unnecessary to obviously change the original HVAC system. By using a simple control circuit, the complexity of the system is decreased. However, the current controller of the variable speed fan that substitutes the PSC motor has the following problems:
1) the function is single and not applicable for different workplaces, for example, operating parameters like the supply voltage and the rotational direction cannot be directly set;
2) the reliability is low; as different workplaces impose different requirements on the variable speed fan, work failures or accident easily occur when the control of the variable speed fan is not adaptable to a certain workplace;
3) the state of each power input line is detected by a current transformer and related circuits, however, the current transformer has large volume and high product costs and occupies relatively large space of the motor controller, thereby decreasing the heat dissipation of the motor controller; and
4) a plurality of sensing units of the current transformer are embedded in a wiring plug of the motor, the installation of which is difficult, thereby lowering the production efficiency and being not beneficial for large scale production.